Nautical Nonsense
by Ilovetoread09
Summary: This is a collection of one-shots centered around my "By the Light of the Moon" AU story. I highly suggest reading that first before venturing into this.
1. Chapter 1

AN: So, my brain just loves this universe. This little story will comprise of one-shots, ranging from short to long, that exist in the "By the Light of the Moon" world, so I recommend giving that a read, if you haven't already, before diving (pun not intended) into this. Anyway, enjoy!

Disclaimer: I don't own Castle.

* * *

Kate scrunches her nose as she fills in the latest form for yet another case file. It's late afternoon, and the homicide floor is quiet, with the exception of Ryan and Esposito ribbing each other about whatever. She can hear them just fine, but she isn't paying attention to any of the words.

Glancing at the computer clock, she notes it's almost quitting time. Just one more file and then she can go home to Castle and begin their romantic date night. Castle's been, or at least should be, writing all day, but she's sure he's spent some of it prepping for tonight. The mere thought prompts a small smile from her. God, she's such a sap.

"What are you smiling about, Beckett? Writer Boy do something right for once?" Espo teases from across the way.

Rolling her eyes, Kate smirks before returning to her paperwork. "Maybe I just enjoy the silence here."

She hears the scoff as her coworker returns to his desk.

"You two are disgusting," he grumbles as he plops down in his chair. "You've been dating for what? Three months? I thought the honeymoon phase would be over by now."

A snort escapes her lips. She is so not telling Espo that the honeymoon phase never really ends, for her kind at least. "I thought you'd be dating Lanie by now," she snips, which promptly shuts him up as he returns to his own paperwork.

She continues her paperwork for a little while longer, until Ryan interrupts her work flow with a fairly alarming question.

"Did the forecast say it was going to rain today?" he inquires.

"Er, no, why?" she asks, gazing up from her desk, her eyes flicking toward her coworker and he gestures outside. She turns to the window, observing the scene outside and that's when she sees it. Storm clouds. Her stomach sinks at the gray sky forming, and the even blacker clouds she can see approaching.

"Looks like it's gonna storm. Weird, huh," Ryan hums. "So, with that, I'm heading home lest I get caught in the downpour. Besides, it's quitting time anyway."

Ryan grabs his jacket from the back of his chair and heads toward the elevator.

"I think I'm gonna head out too," Esposito states, beginning to shut down his workstation.

Kate purses her lips as she stares at the window, raindrops already forming on the glass. Shit.

"I think I'll stick around for a bit," she says and her coworker gives her a nod before heading out himself.

A soft sigh escapes her as she pulls out her phone. Looks like she's going to be late tonight. Her fingers begin to type out the text to Castle, but in the middle of it, he sends her a message of his own.

 _Town car on the way. See you in a bit. ;)_

As her teeth chew at her lip, her face threatens to break out into a grin as she reads the text. Her partner can be so sweet, when he isn't regaling her with his crazy theories, of course.

After closing down her workstation, she makes her way out, bouncing on her heels as the elevator descends to the lobby. The doors open and sure enough, the town car sits outside, rain beating heavily on the its rooftop. Kate sprints, pushes the lobby doors open, and slides into the car just in time. Some rain hit her, but not enough for a transformation, thankfully.

Hopefully, the rest of the evening is just as smooth.

* * *

The town car pulls up to the loft building a few minutes later, and the brunette makes a mad dash to the front, wrenching the door opening and stepping inside. She glances apologetically at a startled Eduardo as she heads up to the loft. As she approaches the apartment, she can smell the delicious meal of...steak, sautéed mushrooms, and potatoes. Mmmm.

"Hey, babe," she greets as she enters the loft, pulling off her jacket and stepping into the kitchen.

"I see your legs are intact," Rick teases, stretching out his arms and pulling her into his embrace before placing a gentle kiss on her lips.

"Thanks for that," she murmurs. "I was going to be late otherwise."

"And we certainly didn't want that," he hums, his chin resting a top her head. "How was your day?"

"Slow, just paperwork. You didn't miss anything. What did you do all day?"

He pulls back, smirking as she raises an eyebrow. "I did do some writing today. In fact, Gina is quite pleased with me." Waggling his eyebrows, he gives her one of his boyish smiles. "Meaning we can enjoy our evening in peace. Which entails a nice home cooked meal, a movie or TV marathon of your choice, a long, hot bath, and some dessert." His voice lowers at the last option, his hands curling around her hips.

"Sounds lovely," she murmurs.

"Now go sit." He gestures toward the island and she obliges, mouth watering as the plate appears in front of her. Good, she's starved!

They enjoy their meal, talking about their day and plans for the week. Touches and gazes are shared as the meal comes to a close. The two clean up before carrying their evening to the couch, flipping through Castle's giant movie and TV collection.

"Mmm, that one," Kate says, curling into her partner who wraps an arm around her. She takes the invite to snuggle closer, her head rubbing against his shoulder in the process.

"Sometimes you remind me of a cat," he comments. "You would look cute as one, probably elegant too." A snort escapes her as a wistful expression appears on his face. "What? You could shrink down, curl up on my chest or sit on my shoulder..."

"Mermaid not enough for you now?" she teases. "You'd rather have something soft and furry to cuddle?"

"No, mermaid is perfectly fine with me."

She turns her head and plants a quick, but passionate kiss on his lips. "Good," she states, clicking the remote for the film to start.

The sit and enjoy the film and each other's company, either snuggling or holding hands as they watch the characters on screen. Once the film draws to a close, Castle rises from the couch to start the water in the tub. Kate follows suit, stripping on the way to the bathroom. It's only the two of them for the night, so she doesn't need to worry about leaving traces of their activities all over the loft.

The tub is big enough that the couple can sit on opposites sides and still move around. However, Castle gets in first, indicating for his partner to sit between his legs. She complies, sliding easily into the porcelain container, her legs morphing into her tail moments later.

"Let me wash you," he murmurs into her ear, and she lets him.

Her tail flicks in delight as he runs the luffa over her skin, gliding over her breasts and torso before moving to her tail. He knows she loves it when he plays with her tail, and this time is no different. His hands gently grasp her fin, massaging along the length, as his lips press against her neck. His ministrations have a pleased hum emitting from her mouth, her body relaxing against him, her tail twitching even more.

Turning her head to gaze at him, she smiles, gently prying the luffa from his hands as his movements slow. "My turn," she purrs, rotating her body so that she's on her stomach facing him, tail up in the air.

Capturing his lips in a languid kiss, she slides the luffa down his neck, his torso, and halts at his stomach. She draws circles on his stomach with the sponge until she slowly descends below his waist, earning a growl from him. Then, without warning, the movement stops and she pulls back, chuckling at his pout.

"Patience," she snickers before reattaching her lips to his skin. Her mouth makes its way down his body until she reaches his stomach. Locking eyes, she winks before dunking her head underwater.

Not needing to come up for air definitely has its perks.


	2. Chapter 2

AN: Here's another. Thank you for all the favorites, follows, and reviews, I really appreciate them! Also, I'm glad people enjoy this universe.

Disclaimer: I don't own Castle.

* * *

Rick wakes, sunlight streaming through his blinds. His hand reaches out for his girlfriend, only to find the spot empty, cold. Lips turning into a frown, he looks around and listens, noting no sign of her, which is odd. She's off today and he'd hoped she'd sleep in late so he could wake her with breakfast in bed and other activities. Maybe she went for a run?

Swinging his legs over the side of the bed, the author throws a robe on and his slippers, padding into the kitchen. He begins to pull out pots and pans, hoping to surprise Kate with breakfast when she returns. And since she's off, he's going all out.

He's halfway through making the batter for pancakes, eggs simmering in a pan on the stove, when the door unlocks. He grins as his girlfriend enters, throwing her keys into the bowl next to the entrance.

"Hey, Babe," she greets, grinning. "Smells fantastic!"

"Hey," he says, giving her a quick peck on the lips when she approaches him. "Breakfast will be ready in a bit." Glancing down at her hand, he notes the plastic bag in between her fingers. "Where did you go this morning? I wanted to wake you up." He makes no effort to hide his pout.

Chuckling, she pulls out a box, which contains a product he's fairly familiar with. "I went to the pharmacy nearby. We forgot to use a condom last night." A teasing eyebrow is aimed in his direction.

Ah, yes. They had become a little overzealous at starting her weekend vacation. Oops.

"I thought you were on the pill?" he inquires.

"Yes, but it's not one hundred percent effective," she reminds him.

"You just want to be certain nothing forms in there?" he assumes, receiving a nod in response as she pops the pill into her mouth. Meanwhile, he pours the batter onto the griddle, lets the pancakes cook and removes the eggs form the pan.

"For now," she states, sighing. He stores that statement away for later. "You see, uh, mermaids are very fertile creatures." Her cheeks tinge pink. "And with you super sperm," he snickers, "I figured we can't be too careful."

"How fertile are we talking?"

"Like, it won't take much effort for me to get pregnant. As far as I know, one try is all we need, basically."

Huh. "Isn't that the same as a regular human though?" That earns him a shake of her head.

"No, humans have a chance in conceiving in one try. For mermaids, it's basically a guarantee." Oh. Smirking at the shock on his face, she continues, "And I'm not ready for that, not yet."

"Not yet?" He grins as he serves her a plate full of eggs, bacon, and pancakes. "So, you want kids?"

"I mean, I want kids with you," she clarifies, taking a bite of her breakfast. "But, it's still early for that, I think. Please, I want to get married first."

He's inclined to agree. They've only been dating for about five months. They may be soulmates, but they're attempting to take their relationship at normal, human pace. That doesn't stop him for staring at engagement rings in the store windows, however.

"Well, whenever you're ready, let me know. We'll go down to the jeweler, pick out a ring."

"You can surprise me if you want," she murmurs, giving him a tentative smile. His eyes widen before flashing a grin. "But don't go out and buy a ring and propose to me tomorrow, please."

His lips form into a playful pout. "Darn it, there goes my plan."

A chortle falls from her lips as she finishes her plate. "One day, Babe, one day."

Sighing, he pictures a child, their child, with her eyes and his hair, and her smile. He knows that the child will be adorable as hell and quite a handful.

"Our little tadpole," he mutters aloud, having gotten lost in his daydream.

"Tadpole?"

"Yeah, like a baby frog. I mean, it has a tail when it starts and it needs water like a mermaid..."

"I'm not a frog," she grumbles, glaring. "You will not nickname our child after a developing amphibian."

"I think it's a cute nickname."

"No, no tadpole. In fact, when the time comes, I am banning all allusions and references to aquatic creatures when it comes to naming our kid."

"You're no fun."

"One of us has to be the killjoy." Stepping around the island, she wraps her arms around his neck, leaning in to give him a slow, languid kiss. "However, we can start practicing now."

"Oh really?" His smile is sly as his hands move to her hips. "I'm more than happy to oblige."

"Just remember to suit up this time." She slips away from him, beginning to walk toward their bedroom.

"Yes, Dear."


	3. Chapter 3

AN: Warning: This covers the topic of abuse, so trigger warning for signs of abuse, so do not read if it makes you uncomfortable. Thank you so mcuh for following, favoriting, and reviewing these little tidbits. I really appreciate it!

Disclaimer: I don't own Castle.

* * *

Rick tosses a lump of pizza dough in the air, grinning as it lands with a satisfied punk onto the counter. Homemade pizza is one of his, and has become one of Kate's favorite, dinners. He normally makes it, but of course she pitches in whenever she wants, particularly when it comes to the toppings. Well, he smirks to himself, he's the one who gets to decide tonight.

Sprinkling cheese onto the dough, he begins to wonder when she'll return. She'd gone out for a swim earlier, and knowing her, she'll lose track of time. As he places the toppings on, his phone pings, signaling a text from Kate.

Might want to make extra for tonight, I'm bringing a guest to dinner.

Furrowing his eyebrows, he tries to think of who it could be. One of their friends, maybe? Shrugging, he pops the pizza in and proceeds to make another, wondering who the mystery guest is tonight.

Just as he finishes the second pie and throws it in the oven, the loft door opens, revealing Kate and another unknown woman.

"Hey, babe," she greets, giving him a chaste kiss on the lips. Her hair's still wet from her swim and he's sure that under her heavy winter jacket, her clothes are still soaking, but he knows she isn't freezing. Stepping back, she gestures to the other woman. "This is Lucy, I met her on my swim." She tosses him a knowing look and he grins.

"Ah, I see," he answers, turning to the black haired woman. "It's nice to meet you, Lucy."

"It's nice to meet you too, Mr. Castle," she chirps, her green eyes shining, her voice like bells to his ears. He knows it's only part of her mermaid allure, but it doesn't make her any less attractive.

"Please, call me Rick," he supplies. "I've made pizza for dinner, no olives, of course." Kate snickers.

"Smells fantastic," Lucy says. "Ooooh, you even put peppers on it!"

"Let me just pull the second pizza out," Rick says, going into the kitchen and removing the second pie from the oven. "You ladies can choose how many slices you want."

The two women grin as they tackle the food. Kate takes her standard two, as does Rick. However, Lucy only takes one slice.

"I'm watching my figure," she explains as Kate raises an eyebrow at the lack of food. Rick almost scoffs, noting that Lucy's fairly thin frame requires more nourishment than watching.

"Wow, I'm usually starving after a swim, but whatever suits you."

Lucy smiles, only offering a shrug as she takes a bite.

"So, where do you live?" Rick asks. "And are you the only mermaid in your family?"

"Rick," Kate scolds. Addressing Lucy, Kate says, "You'll have to pardon my boyfriend. Despite the countless times I've scolded him, he still lacks a filter."

"Ah, but it is something you love about me, Detective."

"Lucky you," the brunette grumbles, starting on her second slice.

The black haired woman giggles, eyeing the couple. "You two are so cute." Then, smiling, she says, "I live downtown with my boyfriend, Sam. And I'm the only known mermaid in my family. My parents figure someone was a mermaid somewhere down the line and I got the gene for it."

"Did your parents take it well?" Kate asks.

"Eventually. I mean it was obviously quite a shock for everyone and since we didn't have any former knowledge, we had to learn everything the hard way, like not going to swim practice." Her green eyes glitter with laughter. "You?"

"I always knew," his girlfriend responds. "So, I guess I'm lucky in that aspect. Is Sam a merman?"

"No, it's just me." Lucy polishes off her crust. Rick can tell she's still hungry as her eyes flicker to the remaining slices.

"Come on, have another piece. Don't worry, neither of us can judge. My darling Kate consumes two whole sets of fries, including a shake and burger mind you, with ease."

Kate scowls. "Says the man who consumed two slices of rich chocolate cake last week."

"It was excellent cake, I will tell you." Kate lets out a noise of disgust and Lucy just watches.

"Thank you, but ah, like I said, I'm watching my figure." Rick swears there's nervousness in her eyes, but it's gone before he blinks.

"Will you at least have some dessert? We have some cherry pie in the fridge," he offers gently.

"Okay," their guest replies, seemingly more to be polite.

The three dig into their pies as they discuss other things and quiz Lucy a little bit more. At eight o'clock, Lucy glances at her phone and stands up from her seat.

"Thank you so much for the meal. Unfortunately, I must get home. Sam doesn't like me out too late, particularly after that stuff last summer. He worries."

"Right," Kate hums. "We should do this again."

"Oh, definitely! Maybe at my place next time."

"It's a date," Rick answers, opening the door for her. Lucy waves goodbye and promises to text Kate at some point.

Once their guest leaves, his soulmate turns to him, concern in her eyes.

"You think something's off, too," he states and she nods. "Do you think it's just her or..."

"I don't know, maybe it's just her personality, or part of the desire to please her soulmate." The brunette rubs her hands over her arms. "I'm concerned though."

"Me too," he says. "If she invites you over to dinner, I'm sure we can make room in both our schedules." He wraps his arms around her, her head resting on his chest.

"Of course." She nuzzles him. "Come on, let's go clean up."

They clear the kitchen, both of their thoughts on Lucy.

* * *

Two weeks later, Rick and Kate stand at the front door of Lucy's apartment, hands full of dessert and wine. Kate knocks and a moment later, the door swings open, revealing Lucy.

"Hey, guys!" she greets, pulling the door open. "Come on in!"

The two enter and Rick notes the white apron the woman wears. Her hair's done up in a bun, making her look like one of those 1950s housewives from the old black and white shows.

"Nice place," Kate states, glancing around the space.

"Thank you. It's Sam's, actually. I moved in a few months ago."

"Though I had wanted her to move in earlier," a voice calls from the living room. The couple turns as a fairly tall man approaches them, his black hair mussed and his blue eyes smiling. "You must be Rick and Kate. I'm Sam, Lucy's boyfriend."

The three shake hands before Lucy gestures for the couple to sit.

"What would you like to drink?" she asks, and the couple answers along with Sam, who requests a beer. As she walks to the kitchen, Sam leans forward, grinning.

"Lucy's told me so much about you guys. However, I gotta know, how did you two meet?"

Rick and Kate glance at each other, chuckling. Kate's the one who tells the story, with Rick interjecting at points, earning him an elbow from his girlfriend.

"Damn, that's far more interesting than our story. I ran into Lucy during a swim and I became enchanted with her instantly. That was about a year ago, and I finally convinced her to move in about four months ago. You guys living together?"

"Not yet," Rick answers. "However, most of her stuff is in my loft anyway."

"I like my own space," Kate defends, rolling her eyes. Lucy returns with their drinks and the couple accepts them with gratitude. "Besides, we need to take it slow."

"Why take it slow when it's true love?" Sam asks.

"Oh, leave them be, Sam." Lucy sighs. "Each couple has their own way of doing things."

"Still don't see the point," Sam grumbles, drinking his beer.

"Eh, we're known to be an odd couple anyway," Rick jokes, kissing the top of Kate's head.

"You're odd," the detective grumbles with affection.

"Well, dinner's almost ready, just need to finish the vegetables," Lucy says. "Anything you guys would like beforehand?"

"Can you get me another beer?" Sam asks, though it comes across more as a demand than a request.

"Of course, Dear." She wanders back into the kitchen.

"So, what do you do, Sam?" Rick inquires.

"Oh, I work for a large firm, usually work big cases, long hours. The usual." Smirking, he eyes the author. "I already know what you do. Famous crime novelist. You're lucky to have snatched this one up, Kate."

Rick senses his partner's internal grimace. "I'm the lucky one. She puts up with my antics and curiosity all day long."

The other man purses his lips before taking another swig of his second beer as Lucy calls the three to the table and begins to serve.

"Looks delicious," Kate comments as a plate of chicken with alfredo sauce, spaghetti, and carrots appears in front of her.

"Tastes great too," Rick concedes, having already taken a bite.

"Thank you," Lucy says, slicing into her own chicken. Her portions are noticeably smaller than everyone else's and her glass is full of water instead of alcohol. Huh, Rick thinks. Though, she may just be unable to drink alcohol for whatever reason.

"Great as always, Dear," Sam says, giving his girlfriend's arms a gentle squeeze.

"So, Lucy, how is your store going?" Kate prods, smiling.

Lucy owns a small, charming perfume shop on one of the busier downtown streets. Rick had visited the previous week, and had even bought a bottle for Kate for Christmas.

"It's going fine. Sales are definitely increasing because the holiday is almost here."

"Won't you be glad to not have to worry about that once we get married?" Rick slides his gaze to Lucy's finger, where a ring is noticeably absent and no indent to show there was one there before he and Kate arrived.

"I like having the store. I created it myself from the ground up," she states, glaring.

"But I can bring the money in," Sam argues. "So, no you won't need the shop." He stares at Lucy, who meets his gaze. Whatever she sees has her shoulders slumping.

"Maybe you're right," she mutters, beginning to clear the plates.

Rick and Kate exchange their own look, both reading the other well.

"Why don't I help you clear?" Kate offers, not taking no for an answer as she helps bring some of the fixings into the kitchen.

"Let's go into my man cave" Sam tells Rick.

Of course, he has a 'man cave'. "Sure."

The two walk down the hall to a room containing typical male hideout furniture. Black leather couches, a flat screen television, a large CD collection, and various posters.

"Want some more alcohol? I've got everything." Sam opens a mini-fridge in the corner of the room.

"No, thank you, I'm good," Rick politely declines.

"Suit yourself." The other man grabs a shot bottle of whiskey from the fridge before closing the door. "So, uh, you and Kate, that's really something."

"Yeah, she's great," the author answers slowly, unsure of what Sam's implying.

"I guess she's the alpha in the relationship." The man plops down on the couch, smirking. "I saw the way you two talked, she definitely likes to take charge."

"We're equals in the relationship," Rick responds. "Yes, she might be a little more upfront, but we balance each other out in the end."

The lawyer chuckles. "Nah. The not moving in thing? That's a control mechanism. She wants to have her own turf."

"She's a private person," Rick answers tersely. "She's used to being alone."

"Whatever you say," Sam chuckles as Rick sits on the couch opposite of him. "I'm just glad Lucy listens to me."

"Yeah, what was that at the table. About her store?"

Sam waves his hand dismissively. "Oh, yeah, that. Just a little influence, that's all. Works wonders when Lucy disagrees with me."

"Influence?" Rick questions, though he's sure he knows what the other man's referring to.

"Yeah, you know, that thing soulmates can do to mermaids." He snickers. "Gets the mermaid to do whatever her soulmate wants with just a look or a word."

Ah, yes, that. He and Kate had discussed it in the past, more as a joke. It never really occurred to him that it could be used to the extent Sam uses it. The thought almost makes the author cringe.

"Oh, yeah. That's not my speed nor is it Kate's." The only enticing he attempts is the kind done in bed, with a very willing Kate. "We prefer compromise." He knows he's taking a low shot, but he doesn't care.

"Meh, like Lucy said, each couple has their own way." Turning the television on, Sam flips to the latest game. "Enough relationship talk. Let's watch some football, like guys."

Rick nods and forces his attention to the screen. He wonders how Kate's faring in the kitchen.

Hopefully better than him.

* * *

"Thank you so much for helping clean up, you didn't have to," Lucy says as she places dishes in the dishwasher.

"I figured you put so much work into the meal, might as well help in some way," Kate responds as she places some spaghetti in Tupperware.

"Thank you." Lucy hums. "I guess the boys are bonding."

Or killing each other, depending on how Castle frames the conversation, Kate thinks.

"Yeah," she murmurs. "So, you and Sam met during a swim?"

"Yep. He scuba dives as a hobby and saw me during one of his trips out on the Hudson," Lucy says, clearly lost in the memory. "We've been attached at the hip ever since. Though, it shouldn't be a surprise, since he is my soulmate."

The woman states the words with such ease that Kate is pretty sure it's true, or at least Lucy thinks it is.

"How did you figure out he's your soulmate?"

"Just a feeling, you know? Also, when he fell down a flight of stairs, I felt some of the impact." With that sentence, all hopes of Kate helping her vanishes.

"Yeah, same thing happened when Castle got kidnapped," Kate says, and the mere thought of how close she had come to losing Castle makes her shudder. "It's frightening, sometimes, how connected you become with your soulmate. The fact that you'd want to die if they died or didn't love you anymore." She isn't sure which one terrifies her more. She knows Castle's love is genuine, but there's still a part of her that worries he'll find someone, someone normal. However, her fears are unfounded and she doesn't entertain them often. But Lucy...

"It's not what you think," Lucy murmurs. Kate blinks in confusion, attempting to school her features. "I saw you looking at my plate and I noticed Rick's reaction to Sam and I's conversation earlier." The brunette raises an eyebrow. "Despite what you see, we're a happy couple. Just different."

"We're just trying to help you," Kate replies.

"I don't need help, don't need saving. I have no problem letting Sam control me a little. He doesn't hurt me." Lucy shakes her head. "He's a little firm and brash, yes, but he loves me all the same."

Sighing, Kate leans against the counter. "But what if he goes overboard?"

"He promised he wouldn't and I believe him."

"Okay, fine, just please let me know if he ever-" Kate starts,, but the other woman cuts her off.

"He won't, but I will tell you if he does," Lucy interrupts. Waving her hand, she says, "Anyway, would you like coffee, tea?"

While not wanting to offend the lovely hostess, the brunette shakes her head. "Ah, no we better get going. I have to go in early tomorrow."

"Okay, then, if you insist."

Just then, Castle and Sam return from the 'man cave'.

"Ready to get going, Castle?" Kate asks.

"Yeah," Castle answers, sauntering over to his girlfriend's side.

"It was lovely having you two for dinner, we should really do it again," Lucy says, her smile genuine.

"Maybe at your place next time," Sam jokes, placing a hand on his girlfriend's waist.

"Thank you for having us," Castle returns. "Keep in touch." He nods to Lucy before he and Kate leave the apartment.

The couple's ride home is silent, the only communication consisting of holding each other's hands.

When they enter the loft, the two turn and look at each other, both sets of eyes containing some emotion neither can name.

"How can someone want that?" Kate asks, more to herself than Castle.

Castle shrugs, even he appears equally disturbed. "They have their way, we have ours."

"I understand that, I just," Kate closes eyes. "I'm afraid he'll-"

"Hurt her?" Castle finishes and she nods. Pursing his lips, he wraps his arms around her, planting a kiss on her forehead as he holds her close. "I'm promise you that I would never take advantage of you."

"I know you wouldn't." She gazes up at him, her arms wrapping around his waist. "I trust you." Her lips graze his. "Love you."

"Let's go to bed," he murmurs as she wraps her legs around his waist and he carries her to the bedroom.

They make slow, tender love, each showing their devotion to the other. Once they lay sated, she snuggles into him, placing her head on his chest.

"I'm still going to keep an eye on Lucy," she murmurs.

"Of course." Castle runs his fingers through the ends of her hair. "Just say the word and I'll do anything you ask to help."

"Thank you, for having my back," she hums before sighing. "However, I'd rather not think about it for the rest of the night." He knows she will anyway.

"Okay," he answers, holding her closer.

Both drift off to sleep, finding comfort in the other's arms.


	4. Chapter 4

AN: Just a little tidbit for this universe. Thanks for continuing to be interested in this unique little world.

Disclaimer: I don't own Castle.

* * *

Kate lounges on one of the pool chairs, taking in some sun with Lanie. She glances up to see Castle and Ryan messing around in the pool. Espo is still putting suntan lotion on himself before diving in.

"It was so nice of you to invite us to your Hamptons house for the weekend, Castle," Lanie says, grinning. Her friend is definitely enjoying the excuse to show off her new, strapless bathing suit. "But damn, did you really need to have that high of a fence? I bet it's blocking a gorgeous view of the ocean."

Kate chuckles, shooting her partner a knowing look. He'd had the high, white fence constructed so she could swim in the pool without any prying eyes. And of course, giving him a private show was an added bonus.

"Well, you know how Beckett loves her privacy..." he jokes, earning a splash from Ryan.

"So didn't need to hear that," he and Esposito groan in unison.

"I think I'm going to hop in too," Lanie states, standing up. "You going to join me?"

The detective shakes her head. "No. Not exactly a fan of water, remember?"

"Right," her friend mutters before shrugging. The ME dives right in, going under before coming back up to the surface. "I thought the case from last summer would've cured that."

Kate shrugs. "Unfortunately, no." Getting up, she checks on the burgers and hot dogs cooking on the grill. Castle, being Castle, of course has some fancy unit that has a thousand knobs, not one of which is clearly marked. "I think the food is done," she announces once she flips the off switch. "Come grab your meal when you're ready."

Castle and Ryan practically leap out of the pool, Esposito and Lanie choosing to stay put for a bit. The two men assemble their meal as the brunette arranges her own plate.

"Damn, this water is nice," Esposito states, treading water. "So warm."

"I always make sure to run the heater first thing in the morning." Taking a bite of his burger, Rick continues, "Plus, the sun also helps keep it warm."

"Mmm, makes it perfect for skinny dipping," Lanie jokes.

"No, no. There will be absolutely no skinny dipping in the pool," Kate orders, tossing a pointed glare at both Lanie and Esposito. "None."

"You're no fun," Espo grumbles.

"Don't worry guys, you can skinny dip when Beckett isn't around," Castle teases.

"I should push you into the pool for that," Kate remarks, lips twitching.

"You can shove me in later," he mutters, smirking. Speaking louder, he says, "You're more than welcome, my dear detective. So long as you join me, of course."

She just rolls her eyes before resuming her spot on the lounge chair.

At least she can soak in some sun.

* * *

Later that night, once everyone else is in bed, Kate sneaks outside to the deck and walks toward the pool. She removes her bathing suit cover, not having bothered with a suit.

"I figured I'd find you out here," her partner chuckles. She can feel his eyes on her,the lust in them.

"Finally getting a chance to swim," she states, slipping into the pool. Within seconds, her tail forms, the scales glittering with the pool lights.

"Mind if I join you?" he asks, though he's already stripping off his shirt.

Her answer is a come hither look as she floats further into the pool. Grinning, he dives in, chasing after her as she dodges his movements. After a moment, she allows him catch her, taking her in his arms.

"Finally by ourselves," he hums. "And I'm sure you've been itching for a swim."

He knows her so well.

"Definitely." She nuzzles his cheek. They just sway for a while, holding each other giving each small pecks here and there. Soon, however, she's craving more and her hand trails down Castle's chest to his hip. "And since we're alone..." she trails off suggestively, tugging at the hem of his swim shorts.

"Why Detective," he starts, but a giggle from somewhere cuts him off.

"Shit! Someone's out here," Kate says, glancing around. She spots Lanie and Esposito coming from the double doors. "Crap!"

Knowing she doesn't have enough time to change back, the brunette dives underwater, attempting to hide as Castle scrambles out of the pool.

She hears Lanie and Esposito sound sheepish when they notice her partner, but still quiz as to why he's out here so late. He gives a lame excuse of having to make sure the pool is clean. Neither of their friends buy it. She so wants to kill him.

One of them approaches the pool and jumps in, the female curves clearly indicating that it's Lanie. And just like earlier, Lanie dunks under water. Kate panics, not having anywhere to go. On top of that, the pool lights illuminate brightly, making the mermaid visible.

Sure enough, Lanie looks in her friend's direction. Her eyes bulge as she spots Kate, eyes trailing down to the woman's tail. If she wasn't so frantic, Kate would find her reaction comical.

"Please don't say anything to Esposito," the brunette begs. "I'll explain everything later."

The ME raises an eyebrow glancing down at the purple tail again before returning to the surface.

The mermaid breathes a sigh of relief when she hears Lanie tell Esposito that the pool does look a little murky. He grumbles before walking back inside. Figuring she's safe, the brunette resurfaces, Lanie and Castle staring down at her.

"How long have you known?" The ME quizzes Castle.

"Since last summer," Castle supplies, shooting an apologetic look at his girlfriend.

"Of course," Lanie huffs. Turning her attention back to the woman in the pool, she says, "You and me are going to have a long talk, tomorrow. When I'm wide awake and can assure myself that this isn't some crazy dream." She begins to walk away before stopping and turning around. "Your tail looks fabulous, by the way." She winks before heading back inside.

"At least I won't have to explain why I avoid pedicures anymore," Kate says.

Her partner laughs, handing her a towel. "At least she took it well."

"Well, we'll find out tomorrow," the mermaid grumps.

Mathias was so not going to be happy about this.


	5. Chapter 5

AN: Here's another peek into this universe!

Disclaimer: I don't own Castle.

* * *

"Do you really think he's still here?" Castle asks, referring to their latest suspect.

"Only one way to find out," Beckett replies, gun in hand, vest on as she, him, Ryan and Esposito approach the apartment door. The team is currently on the case of the murder of a thirty year old woman who had been shot dead in her apartment. Her partner had played the part of distraught husband very well. Unfortunately for him, his bank records exposed him for the fraud he was as large amounts of withdrawals followed up by purchases of jewelry for a mistress had him climbing back to the top of the suspect list. Additionally, video footage of him dumping the murder weapon solidified the team's sights on him.

Knocking on the door, Beckett calls out, receiving no answer. Signaling Esposito, the detective kicks the door in and the four swarm the apartment, clearing each room as they check.

As Rick and his partner wander into the bedroom, he states, "He must have-" However, he's cut off by Beckett placing a finger to her lips, her other hand gesturing toward the closet. Oh, she must hear something inside.

"I guess you're right, Castle, he must not be here," she says, raising an eyebrow as she throws the door open, revealing their suspect. Eyes wide with fright, clearly acting on instinct, the suspect points his gun at Beckett, and knowing what's coming next, Rick pushes her out of the way, the shot going off just as his partner hits the ground.

Everything else happens in a blur. Pain radiates from what feels like his whole torso, but Rick knows it's only his upper chest that's been hit. The close proximity of the gun means that the bullet ripped through the vest, striking his body. As he collapses, he can hear the boys rush in, dragging the guy away from the window he attempts to escape from, pinning him down and cuff him to the nearby radiator. Beckett leans over her partner, putting pressure on the wound to slow the bleeding.

"Beckett, the paramedics are fifteen minutes away," Espo says as Rick's vision begins to blur.

"No, c'mon Castle, stay with me," she says, one hand moving to his cheek. "He doesn't have fifteen minutes!" He feels himself begin to go in and out of consciousness, Beckett shaking him to keep him alert. "Espo, Ryan, one of you get me some water, and pliers or tweezers."

Water? What does she need water for-Oh. Oh no.

"Beckett," he begins to say, words slurring. "You don't have to, the ambulance will be here."

"Not enough time, " she mumbles, removing his vest and ripping open his shirt.

"That was my favorite shirt," he grumps, earning, from what he can tell, a smile from his partner.

"You can get another one." Now, someone else is in the room, based on the extra footsteps he can hear. Ryan.

"What are you gonna do, Beckett?" Ryan asks. "You can't take the bullet out, he'll just keep bleeding."

"Yeah," Esposito this time. "There's nothing you can do for him right now."

"Yes there is," she snaps, taking a pair of tweezers from Ryan and a sizable glass of water from Espo. "I can help him."

"Beckett, stop-" Rick begins, but she cuts him off.

"I want to do this, I can do this."

He gazes at her, seeing fear, but also determination in her eyes. He nods in acceptance as she takes the tweezers between her fingers.

"Guys, hold him down," she murmurs apologetically. He feels their hands on his arms as Beckett starts to prod his wound. He hisses, the contact of the instrument to the injury causing excruciating pain. He knows her eyesight is superior and that she'll have no trouble finding the bullet. However, panic still seizes him as she clamps down on the bullet and slowly removes it.

"Beckett," he says.

"Shush," she snaps, her face set in deep concentration.

So, he remains silent as she pulls the bullet out. The wound throbs and he's unsure of how much blood he's lost.

"Water, please," she instructs.

One of the boys hands her the water and without any warning, she begins to chant, the water slowly moving toward her fingers.

"What the hell?" Ryan mutters.

"Beckett, what are you doing?" Espo demands.

She ignores them, continuing her chanting, moving the water over his wound. He feels the coolness of the liquid hit the hole in his chest and is instantly soothed. Beckett keeps chanting, panic creeping into her words. With some effort, he turns his head, realizing that the glass is half empty.

"You can do it," he murmurs, locking his eyes with hers. "I know you can do it. Besides," he huffs out a breath. "who else would annoy you all day?"

She tosses him a narrowed glance, but his words seem to do the trick as he feels the burning slowly recede, the pain evaporating, his breaths easing. Soon, Beckett's chanting ceases and she positions him upright against the closet door.

"How do you feel?" she asks, gazing into his eyes, apparently relieved at whatever she sees in them.

"Much better," he says. Looking around, he notes that there's blood everywhere, from the floor, to the bedding, the closet door, and Kate's hands and clothes. The boys have some blood on them as well, their shoes covered in the substance.

"You're going to need a blood transfusion," she states. "I don't know how, and don't really know if I can, regenerate blood."

"Woah, are you like a witch?" a voice asks. It's then that the four look over to the radiator, having forgotten all about their suspect.

Walking over to him, Beckett towers over the man. "You saw nothing, got it? Otherwise, I'll put a spell on you that won't be pleasant." Rick holds back a laugh as the guy shrinks, nodding. "Good."

Seconds later, the familiar whirl of sirens approaches and the relief in the team is palpable. Soon, Rick is loaded into an ambulance, Kate right behind him.

"You know we're gonna want a real explanation, right?" Esposito asks.

"Let's make sure Castle is settled in first, okay?" The boys just nod as the vehicle's doors close.

"How much will you tell them?" Rick asks.

"Might as well tell them everything. That way I can finally swim in front of them." She rolls her eyes, clearly recalling their Hampton weekend where she couldn't really swim due to her secret. Lanie found out during that little vacation and kept her lips sealed ever since.

He's sure Ryan and Esposito will be the same, with some teasing, of course.

* * *

They arrive at the hospital and Rick is immediately placed in a room, the nurses on the hunt for his blood type. They return shortly, hooking him up to an IV, giving him some medication to ensure he doesn't get a reaction, and start the infusion. He needs a fair amount, apparently.

As soon as he's settled in, Beckett rubs his free arm in comfort, before punching it, hard.

"Ow! What was that for?" he howls, the door to his room shut, thankfully.

"That was for jumping in front of me! You knew the bullet wouldn't hurt me!" She's glaring, but he can see the underlying worry in her irises.

"I panicked, okay? I saw the gun and didn't want you to get shot, momentarily forgetting that you're invisible."

She lets out a light snort before scowling. "I could have lost you! What would have happened if I couldn't heal you? Or the ambulance arrived too late? What would I say to Alexis or your mother if I lost you during a case?"

"But that's always been a risk. We both know that," he murmurs. Taking his free hand, he links his fingers with hers. "But I promise to not jump in front of a gun for you again."

Kate's face brightens into a smile. "Good. Besides, only I can do that."

"Show off," he mutters, making her chuckle.

There's a knock on the door and Ryan and Esposito poke their heads in.

"Can we come in or are we interrupting a love fest?" Espo jokes.

"You can come in," Kate answers, smirking.

"You feeling okay, Castle?" Ryan has the decency to ask before jumping right in.

"I'm all good, feel even better as I get blood back in."

"Cool," Espo says. Glancing at Beckett, he starts "So…."

"Bro, we can wait," Ryan objects, but Kate waves him off.

"It's fine. I'll tell you guys everything, but it's going to take a while."

"Well, looking at Castle's blood bag here, we've got time," Ryan jokes.

So, Kate tells them everything, from her childhood, to the prior summer when she and Castle met, to today and everything that entailed. By the time she's done, the boys sit in stunned silence, absorbing everything.

Rick's the first one to break the silence. "See, Espo, you weren't too far off with the description of Beckett's mermaid form." Ryan laughs as Esposito's cheeks tinge a slight pink.

"Okay, you two, anything else?" Kate inquires with a raised eyebrow.

"Since you're soulmates, does that mean you're going to look at each other with goo-goo eyes forever?" Esposito asks.

"Yep!" Rick smirks.

"Great," the detective mutters, disgust filling his face.

"Alright, alright," Ryan says, patting his partner on the shoulder. "We should get back to the precinct and start filling out the paperwork. Let these two lovebirds revel in each other for a bit."

"Yes, the very heavily edited paperwork," Espo teases, winking at Rick and Kate.

The two exit the room, leaving the couple to themselves.

Rick glances at his partner, noticing her tense shoulders, her somewhat still anxious expression.

"Go for a swim," he says, knowing it's her best method for clearing her head or relaxing. "I'll be here for a few more hours."

"You sure?"

"Yeah. I'll be fine. Besides, I have lovely nurses to dote on me."

"Ha ha." She kisses his forehead. "Be back soon."

"Bye."

Once she leaves, he leans back, glancing at the bag filled with blood. Definitely still have a long way to go.

Taking out his phone, he smiles, looking at the candid photo of Kate he set as his lock screen, where she is smiling at something on her computer at work. He still can't believe she chose him and that they fit together so perfectly. Sure, they have their fights and silly little arguments about certain habits and eccentricities, but at the end of the day, they love each other.

That's why he has a ring encased in velvet hidden in his writing desk, the one place Kate would never look. He plans on proposing soon, he just doesn't know when exactly.

What he does know is that he loves Kate with every fiber of his being and he wants to spend the rest of his life with her.

Even if Ryan and Esposito get irritated by their eternal love fest.


	6. Chapter 6

AN: Here's more of this universe! Thank you for all the follows, favorites, and reviews for this story!

Disclaimer: I don't own Castle.

* * *

Kate and Rick stand side by side, staring at the ocean, toes digging in the sand.

"Ready for a swim?" she asks, grinning.

"Yep," he returns the smile as they wade into the water until they're both under. She forms his oxygen bubble after giving him a quick kiss.

"Hold on tight," she reminds him as her arms wrap around him and they're off, the speed at which the couple goes turning everything into a blur.

Soon, the water clears, telling Rick that they've reached their destination. They swim along the usual pathway until they reach the pristine buildings of Atlantis. The ancient city doesn't change much in structure, but the merpeople come and go often.

"I need to see Mathias for a minute," Kate says as the duo swims along, the merpeople eyeing them. While Rick's been there numerous times, he's still considered an oddity in the community. The people are nice enough, but highly suspicious of him.

Kate nods hello to the two guards, both of them tossing friendly smiles her way and giving Rick fist bumps. When they swim into the throne room, Mathias sits in his seat, eyes on the duo as they enter.

"Hello Katherine, Richard." He gives them both nods. "I hope everything is well."

"Yes," Kate says. She then proceeds to give him an update on the surface world, which isn't much.

"I'm glad to see that everything has settled down up there." Eyes turning toward Rick, Mathias raises his eyebrows. "And how have you been Richard?"

Rick smiles easily, not bothered by the implication behind the question. "Great! About to have another book launch, in fact."

"Ah, yes," Mathias says with amusement. "Katherine told me you had finally finished your newest book. She's absolutely raved about what she's read."

"Have not," Kate mumbles, but her cheeks turn pink.

"Well, that's excellent to hear." The author smirks. "Perhaps I can give you a copy somehow."

The king waves a hand. "Don't bother. I have no interest in the human world, particularly the highly depraved part."

Rick sighs, knowing there's no way to change the elderly man's mind. "Of course."

"Anyway, I have several appointments for today. Thank you for coming, Katherine. I will see you soon."

"See you next time, your Highness," she says, both of them bowing before leaving the throne room.

"He still doesn't like me," Rick grumbles.

"He doesn't trust any human, don't take it personally." She grabs his hand as they glide through the city. "Besides, as long as he doesn't interfere with us, who cares."

"Right," Rick mutters. He's still bummed that the king can't warm up to him, regardless of what the author does.

"Anyway, let's visit the grotto."

"Okay!" Rick grins, happy to see that she's feeling sentimental today. It works perfectly for him.

They swim, more like float, along the area, enjoying the scenery of colorful plants and fish, holding hands. He knows it's a unique version of a romantic walk, and he wouldn't have it any other way.

And he hopes to do it for the rest of his life.

* * *

They arrive at the grotto and he takes his usual seat, glancing at the pictures. He knows the stories behind each of them now, Kate having weaved each tale on various visits. His imagination still runs wild sometimes, though, and he imagines different backgrounds for some of the images.

"I still miss my mom sometimes when I'm here, usually when I'm alone," she says, sitting next to him. "But you always make it better."

He would kiss her, but his need for oxygen prevents him doing so.

"And I hope I continue to make you happy." He smiles. "After all," he starts, digging into the pocket of his swim trunks. "We are soulmates." Holding out his hand, he opens the velvet box that he's been holding onto for months. He hears her gasp slightly as he does a semi-kneel.

"Kate, I love you, and want to be with you for the rest of our lives, well mine at least." They both chuckle. "I know we're soulmates, but I want this to be your choice. So, will you do me the honor of marrying me and becoming my partner for life?"

She grins, her eyes shining with happiness. "Yes," she murmurs. "Yes!"

With that, he slides the ring on her finger and unable to resist, kisses her fiercely and twirls her around. Kate laughs, one of the most beautiful sounds he's ever heard. However, he can feel his airways tightening and so does Kate as she makes quick work to construct another bubble.

"Come on, let's get going before your airways really burst," she says, leading him out of the grotto.

They speed swim back to surface, right where they started. As soon as they break the water, they kiss for real, long and slow.

"Come on, let's dry off and head back," Kate says, resting her forehead against his.

"I'm sure my mother already has champagne ready and halfway finished."

His partner rolls her eyes. "Har har. Give your mother a bit of a break."

"Yes, dear."

She elbows him as he carries her to a nearby rock. They're far away from prying eyes, so she's safe. As they wait for her legs to return, he notices her gazing at her ring, playing with it in the sun. It glitters as much as her tail does. Huh. He didn't think she'd be that focused on it.

"Everything okay?" he asks.

The smile she gives him is genuine. "Yeah, just I'd never thought I'd find my soulmate. Now, I can't believe I'm wearing an engagement ring."

He cups her face with his hands, looking into her eyes, hoping she sees the love in his. "I'll try to make sure you believe it every day." He places his lips on hers, hands beginning to roam. She chuckles.

"No beach sex. Sand is no fun to wash off," she reminds him. Right. The last time they made love on the beach they were finding sand in the most unfortunate places days after.

"Later then," he murmurs before gathering their belongings. "Come on, let's go home."

"Yeah," she states, wrapping an arm around his waist. "Let's go home." He glances at the ring on her finger, and then her. With her hair dripping wet, sticking to her face, her smiling at him looking utterly blissful, it's one of the most beautiful sights he's ever seen.

He knows he's already home.


End file.
